This invention relates to a process for mounting a semiconductor device on a wiring board. More particularly, it relates to a process for mounting a semiconductor device whereby a bare chip is directly mounted on a substrate by using an anisotropic conductive adhesive film.
To mount a bare chip directly on a wiring board such as a print wiring board, there has been known a process with the use of an anisotropic conductive adhesive film having conductive particles dispersed in a binder.
In this process for mounting a bare chip on a wiring board by using an anisotropic conductive adhesive film, it has been a practice to form protruding bump electrodes in the Semiconductor device side or in the wiring board side.
This is because, in case of bumpless connection without forming any bump, conductive particles sometimes come into contact with the scribe line at the edge of the Semiconductor device thereby causing a short-circuit.
In recent years, there has been required fine pitching between the electrodes of a wiring board of the above type. To satisfy this requirement for fine pitching, the connection electrode area between the wiring board and the Semiconductor device should be reduced.
To achieve fine pitching in practice in the conventional mounting process, it is necessary to surely provide conductive particles between the electrodes. To ensure the existence of the conductive particles, it is suggested, for example, that the conductive particle diameter is further reduced so that a larger number of conductive particles can be contained in the binder of the anisotropic conductive adhesive film.
However, an increase in the content of the conductive particles in the binder is accompanied by an increase in the viscosity of the anisotropic conductive adhesive film and, in its turn, a decrease in the fluidity of the conductive particles in the binder. As a result, it becomes difficult to uniformly disperse the conductive particles in the binder. At the same time, there arises another problem that the insulation properties of the anisotropic conductive adhesive film are deteriorated.
When the conductive particle diameter is reduced, on the other hand, the absolute deformation caused by crushed conductive particles in the step of the thermocompression bonding becomes smaller and thus the irregularity in the bump electrode height cannot be compensated thereby. In such a case, it is feared that some of the electrodes of the wiring board and the Semiconductor device undergo connection failure and thus the conduction reliability is lowered.
As discussed above, fine pitching cannot be sufficiently established in practice in the conventional mounting processes.
To solve these problems, there is pointed out a process which comprises tentatively thermocompression bonding a conductive particle-free insulating adhesive film to a wiring board, then forming a concave in the insulating adhesive film by using, for example, a press head almost as large as the outer size of an Semiconductor device, and then putting an anisotropic conductive adhesive film in the concave and thermocompression bonding the same.
By using this mounting process, conductive particles can be densely provided between the Semiconductor device and the wiring board and thus connection electrodes can be electrically connected to each other without fail while maintaining the content and diameter of the conductive particles at the levels comparable to the existing cases.
In this case, however, it is necessary to provide a press head for forming the concave in addition to a compression bonding head, which makes the constitution of the apparatus complicated.
In case of mounting Semiconductor devices of various sizes on a wiring board as in a multi chip module (MCM), it is necessary to prepare plural press heads corresponding to the outer shape of each Semiconductor device, which makes the apparatus constitution further complicated. In this case, there arise another problems that an apparatus of a larger size is needed and a longer time is consumed in replacing the press heads during the mounting operation.
An object of the present invention, which has been completed to solve these problems encountering in the conventional art, is to provide a process for mounting a semiconductor device and a mounting apparatus whereby electrodes of a fine-pitch semiconductor device and a wiring board can be surely connected to each other.
Another object of the present invention is to provide a process for mounting a semiconductor device and a mounting apparatus whereby the occurrence of a short-circuit between the semiconductor device and the wiring board can be prevented in a bumpless IC chip.
Another object of the present invention is to provide a process for mounting a semiconductor device and a mounting apparatus whereby semiconductor devices of various types can be easily and quickly mounted on a wiring board.
According to the present invention, which has been made to achieve the above-mentioned objects, provides a process for mounting a semiconductor device by electrically connecting an electrode of the semiconductor device to an electrode of a wiring board by using an anisotropic conductive adhesive film having conductive particles dispersed in an insulating adhesive, which process involves: the step of tentatively thermocompression bonding a conductive particle-free filmy insulating adhesive onto a wiring board to thereby form an insulating adhesive layer; the step of forming a concave of a predetermined size in the insulating adhesive layer by using a compression bonding head provided with a pressing chip at a predetermined position; the step of putting in the concave of the insulating adhesive layer an anisotropic conductive adhesive film of a predetermined size; and the step of mounting a predetermined semiconductor device at a predetermined position of the compression bonding head and then positioning the semiconductor device and thermocompression bonding to the wiring board.
In thermocompression bonding with the use of an anisotropic conductive adhesive film, it is generally observed that conductive particles tend to run off together with the insulating adhesive toward the edge of the Semiconductor device. In the case of the present invention, however, the conductive particles tending to run off along the Semiconductor device edge are blocked by the brim of the concave formed in the insulating adhesive layer. Thus, the conductive particles scarcely flow in the direction of the Semiconductor device edge.
According to the present invention, therefore, the conductive particles can be densely held between the semiconductor device and the wiring board. Thus, plural conductive particles can be provided on each electrode at an extremely high probability and connection electrodes can be surely electrically connected to each other without fail even in a case where connection electrodes are located at very small intervals.
According to the present invention, moreover, no conductive particle reaches the scribe line of the Semiconductor device edge and, therefore, there arises no short-circuit between the scribe line and the wiring board.
According to the present invention, furthermore, a concave is formed in the insulating adhesive layer by using a press head provided with a pressing chip of a predetermined size. Accordingly, it is unnecessary to use many press heads respectively depending on the outer shape of Semiconductor devices, even in case where Semiconductor devices of various types are to be mounted. Thus, the apparatus constitution can be simplified.
In this case, it is also effective in the present invention that the press head serves both as the compression bonding head in tentatively thermocompression bonding the insulating adhesive, forming the concave and thermocompression bonding the semiconductor device with anisotropic conductive adhesive film.
According to the present invention, the press head for forming the concave can be omitted, which contributes to the further simplification and down-sizing of the apparatus constitution.
On the other hand, the preset invention relates to an apparatus for mounting a semiconductor device on a wiring board provided with a compression bonding head for electrically connecting an electrode of the semiconductor device to an electrode of the wiring board, characterized by having a press head provided with holding means whereby a pressing chip for forming a concave of a predetermined size in the insulating adhesive layer in the wiring board side and the semiconductor device are held respectively.
According to the present invention, the above-described process of the present invention can be easily carried out.
In this case, the apparatus constitution of the present invention can be further simplified and down-sized by constructing the compression bonding head as serving both as the press head.
Moreover, the apparatus constitution of the present invention can be further simplified and down-sized by constructing the holding means as holding respectively the pressing chip and the semiconductor device in a removal manner.
As the holding means in this case, the apparatus of the present invention may be constructed as sucking the air via a suction hole formed in the compression bonding part of the compression bonding head, for example.
Owing to the above-described constitution, the pressing chip can be easily and quickly attached/removed by switching the air suction. In addition, it also becomes possible to mount members of various shapes onto the compression bonding head.
It is also effective that, in the present, the face of the pressing chip in contact with the insulating adhesive layer is releasable from the insulating adhesive.
According to the present invention, the releasable face of pressing chip prevent stripping the insulating adhesive layer from the wiring board caused by adhering to the pressing chip.